Differentiated roles of Lifshitz transition on thermodynamics and superconductivity in La <sub>2-</sub> <i> <sub>x</sub> </i> Sr <i> <sub>x</sub> </i> CuO <sub>4</sub>
Yong Zhong, Zhuoyu Chen, Su-Di Chen, Ke-Jun Xu, Makoto Hashimoto, Yu He, Shin-ichi Uchida, Dong-Hui Lu, Sung‐Kwan Mo, Zhi‐Xun Shen
Abstract
The effect of Lifshitz transition on thermodynamics and superconductivity in hole-doped cuprates has been heavily debated but remains an open question. In particular, an observed peak of electronic specific heat is proposed to originate from fluctuations of a putative quantum critical point p* (e.g., the termination of pseudogap at zero temperature), which is close to but distinguishable from the Lifshitz transition in overdoped La-based cuprates where the Fermi surface transforms from hole-like to electron-like. Here we report an in situ angle-resolved photoemission spectroscopy study of three-dimensional Fermi surfaces in La 2- x Sr x CuO 4 thin films ( x = 0.06 to 0.35). With accurate k z dispersion quantification, the said Lifshitz transition is determined to happen within a finite range around x = 0.21. Normal state electronic specific heat, calculated from spectroscopy-derived band parameters, reveals a doping-dependent profile with a maximum at x = 0.21 that agrees with previous thermodynamic microcalorimetry measurements. The account of the specific heat maximum by underlying band structures excludes the need for additionally dominant contribution from the quantum fluctuations at p* . A d -wave superconducting gap smoothly across the Lifshitz transition demonstrates the insensitivity of superconductivity to the dramatic density of states enhancement.